And maybe it's overkill, but here's his article from his blog specifically on cocoa powder (
http://winemaking.jackkeller.net/wineblog19.asp):
"If you have shopped for cocoa powder in any sizeable supermarket, you probably know there are choices. But if your choices are between Baker's, Hershey's and Nestle's, you might consider looking for a larger supermarket. Even then, your choices may be limited but could open up a couple more brands. Why is this important? Because all cocoa powder is not the same, and if you are making a base-chocolate wine, you want the right kind.
At the most basic level, there are essentially two kinds of cocoa -- natural and "Dutched." Dutch-process cocoa powder is made from cocoa (actually, cacao) beans that have been washed with a alkaline solution to neutralize their acidity. Natural cocoa powder is made from cocoa beans that are simply roasted, pressed to extract at least half the cocoa butter and then pulverized into a fine powder.
Natural cocoa powder and chocolate contain more antioxidants because the "Dutching" process removes some; "heavy Dutching" removes as much as 90%. However, experts tell us that cocoa is so rich in antioxidants that removing 90% still leaves it in the "super-antioxidant" class of foods.
Natural cocoa powder has a richer, more acrid aroma, but accordingly has a more acidic and bitter taste. Contrary to intuition, natural cocoa powder is lighter in color and more difficult to dissolve in water. Dutch-processed cocoa has less acidity, a smoother flavor and darker, redder color, and it is also more soluble, which is really important when making wine. .
So, which kind is best for integrating into wine. If you are used to making base-chocolate wines from natural cocoa powder and know how to adjust the amount to balance the acidity, then natural cocoa is probably your best choice except with more delicately flavored base ingredients like strawberry, kiwi, mint, nectarine, and peach. These bases can easily be overwhelmed by a rich, natural cocoa flavor and leave you wondering what the base actually was.
The first time I made strawberry-chocolate wine the strawberries were frozen slices and very flavorful, but I only used 2 1/2 pounds and a rich natural cocoa. Only the aroma hinted at what was under the chocolate. Still, the aroma was so intense that everyone "tasted" strawberries when in reality they didn't. This was proven when we all pinched closed our noses while drinking the wine and all but one admitted not being able to discern the strawberries.
When it comes to baking with cocoa powder, the type you use is dependent on the recipe. If it calls for natural cocoa powder, you must use it or risk having a flat or dry product. Natural cocoa, you'll remember, is more acidic. As a result it reacts with baking soda and causes a leavening (rising) action within the batter and finished baked goods. If the recipe isn't clear on which type to use but calls for baking soda, use natural unsweetened cocoa powder. If the recipe leaves out baking soda but includes baking powder, use a Dutch-processed cocoa powder. It's all in understanding what various ingredients do for a recipe. The same applies to winemaking recipes.
The following are some of the Dutch-processed cocoa powders I've identified, although most will never cross your path in a supermarket. I have only found the Hershey's, Ghiridelli, Lindt, and Penzeys. I am told the U.S. military commissaries occasionally carry Pernigotti and Van Houten but I honestly have never looked for them when I shop there. However, you can buy any of them (and a lot more) online. As I said, these are some:
Bensdorp Cocoa Powder "Royal Dutch"
Callebaut Belgian Chocolate "Belgian Cocoa Powder"
Droste Cocoa Powder
Ghiridelli Chocolate Dutch Process Cocoa Powder "Superior"
Ghiridelli Chocolate Dutch Process Cocoa Powder "Sunrise"
Guittard Cocoa Powder, Full Dutched Process "Jersey Cocoa"
Guittard Cocoa Powder, Full Dutched Process "Perfection Cocoa"
Hershey's Special Dark Dutch Processed Cocoa Powder
Lindt Dutch Process Cocoa
Michel Cluizel French Chocolate Dutch Processed Cocoa Powder
Penzeys Dutch Process Cocoa
Pernigotti Dutch Processed Cocoa Powder
Poulain Dutch Cocoa Powder
Rademaker Dutch Processed Cocoa
Ramstadt-Breda Medium Dark Cocoa (France)
Ramstadt-Breda Rich Dark Cocoa (Holland)
Valrhona Pure Unsweetened Cocoa Powder
Van Houten Premium Dutch Cocoa
There are also some non-branded, generic Dutched cocoa powders that reportedly are high quality. Most notable of these are Pier 1 Imports, Trader Joes and nuts.com. But they also sell natural cocoa powders, so read the descriptors carefully or ask before you buy.
I do think I will splurge soon and order some Valrhona Pure Unsweetened Cocoa Powder online. Absolutely every authority I've read rates it as the very best...with a price to match. But I know I am mortal and would like to taste the very best once before I check out.
One last thing, most of the online recipes for base-chocolate wines were ripped from my site or adapted from my 2007 recipes. I don't really care about that except if you copy you are supposed to attribute the source. My greater concern is that most copiers and adapters see "4 oz Hershey's Cocoa Powder" in the ingredients but fail to notice (or understand) the following: "I measured the cocoa powder in dry ounces...." Over and over again I see the cocoa in the ingredients listed as "4 oz (1/2 cup) Hershey's Cocoa Powder". There is a huge difference between a half cup and 4 ounces by weight. Four ounces -- that's 114 grams -- of cocoa powder is a lot more than a half cup, in which case you may very well want to use Dutch processed cocoa powder."